Gram-negative bacterial cells are surrounded by a double layer of membranes, i.e., the outer membrane and the inner, cytoplasmic membrane. The outer membrane, which is a part of the cell wall, is composed of proteins, phospholipids, and lipopolysaccharide. The major objectives of this project is to understand (a) the supramolecular architecture in the outer membrane, (b) the functions of the outer membrane, especially its permeability properties, and (c) the mode of assembly of the outer membrane, i.e. how the macromolecules could be assembled in a proper manner in living cells as well as in cell-free systems. Since lipopolysaccharide is a characteristic component of the outer membrane, its structure and biosynthesis will also be studied. In the latter area, the main objective of our work will be to elucidate the molecular basis for the alteration of cell surface, with a view that the frequent alteration of lipopolysaccharide structure in Salmonella might serve as a model for surface alterations in tumor cells.